Manufacture of zinc hyposulphite



, ple as zinc bisulphite, are suitable.

Patented June 11, 1940 UNITED MANUFACTURE or zmo nrrosorrnrrc Rolf Luehdemann, Ludwigshafen-on-the-Rhinc, Germany, assignor to l. G. Farbenindustrie Aktiengesellschaft, Frankfort on the Main,

Germany No Drawing. Application April 1, 1938, Serial No. 199,445. In Germany April 20, 193'? 4 Claims.

ture of concentrated solutions of zinc hyposulphite.

It is already known that zinc hyposulphite is formed by the action of sodium bisulphite solutions on zinc amalgam. It is impossible, however, to prepare in this way concentrated solutions of zinc hyposulphite suitable for the working up to solid sodium hyposulphite because difficultly soluble salts are formed as icy-products.

) The action of sodium bisulphite solutions on zinc amalgam in the presence of free sulphurous or sulphuric acid gives worse yields of zinc hyposulphite, while diflicultly soluble salts are also obtained.

5 I have now found that zinc amalgam may be converted in a very simple and smooth manner into zinc hyposulphite by causing sulphur dioxide to act on zinc amalgam in an aqueous medium in the absence of alkali salts. The reaction may substantially be represented by the equa- In this way it is possible to prepare concentrated zinc hyposulphite solutions containing about 400 grams of zinc hyposulphite per liter with a yield based on zinc of from 65 to 80 per cent without substantial amounts of difficultly soluble salts being formed. A certain amount of mercury sulphide is formed by decomposition of a small portion of free hyposulphurous acid.

Still higher yields based on zinc may be obtained by carrying out the reaction in the presence of small amounts of buffer substances. For

i this purpose zinc salts of Weak or medium strength acids, as for example bisulphite, sulphite, malonate or malate of zinc, and basic zinc compounds, as for example hydroxide and oxide of zinc, which during the reaction pass into solution for exam- By working in this manner concentrated zinc hyposulphite solutions containing about 400 grams and over of zinc hyposulphite per liter are obtained without any form of mercury sulphide taking place. The

. concentrated zinc hyposulphite solutions obtained may be worked up in known manner to solid sodium hyposulphite.

The following examples will further illustrate how the said invention may be carried out in practice but the invention is not restricted to these examples. The parts are by weight.

Example 1 29.4 parts of zinc in the form of amalgam are covered with 120 parts of water and 4'7 parts of sulphur dioxide gas are led in while stirring. During the reaction there is a temporary yellow coloration due to free hyposulphurous acid.

still contains 6.0 parts of zinc. hyposulphite are obtained. The concentration is The present invention relates to the manufac- Some mercury sulphide then separates out. The whole of the zinc contained in the amalgam is converted. 56.8 parts of zinc hyposulphite are obtained. The concentration amounts to grams of zinc hyposulphite per liter and the 5 yield, with reference to zinc, is 65 per cent.

Example 2 18.4 parts of zinc in the form of amalgam are covered with 75 parts of water and 26 parts of 10 sulphur dioxide gas are led in while stirring.

A small amount of mercury sulphide separates out. The amalgam remaining after the reaction 29.5 parts of zinc 347 grams of zinc hyposulphite per liter and the yield, with reference to zinc, is 80 per cent.

Example 3 18.1 parts of zinc in the form of amalgam are added to a solution of 4.5 parts of zinc malonate in 75 parts of water and 31 parts of sulphur dioxide are led in. The solution remains practically colorless and mercury sulphide is formed only in traces. The residual amalgam contains 1.7 partsof zinc. 42.5 parts of zinc hyposulphite are obtained. The concentration is 434 parts of zincfhyposulphite per liter and the yield, with reference to zinc, is 87 per cent.

Example 4 l Sulphur dioxide gas is led while stirring into a suspension of 2 parts of zinc oxide in '75 parts of water until the zinc oxide has dissolved. 24.4

parts of zinc in the form of amalgam are then added and another 30 parts of sulphur dioxide 35 gas are led in. The solution remains colorless. No .mercury sulphide is formed. The residual amalgam contains 9.5 parts of zinc 41.2 parts of zinc hyposulphite are obtained. The concentration is 462 parts of zinc hyposulphite per liter and l the presence of a member of the class consisting of Zinc oxide and zinc hydroxide acting as a buffer substance.

4. In a process as in claim 1 the working in 5 the presence of a salt of zinc with from weak to medium strength acid as a buffer substance.

ROLF LUEHDEMANN. 

